Methods for producing aromatic carboxylic acids include a method of oxidizing an aromatic compound having an alkyl group on its aromatic ring, such as xylene, with molecular oxygen in an organic acid in the presence of a Co—Mn—Br catalyst. This method, however, uses highly corrosive bromine and must thereby use production facilities of special materials.
Japanese Unexamined Patent Application Publication (JP-A) No. Hei 08-38909 and JP-A No. Hei 09-327626 propose oxidation catalysts comprising an imide compound having a specific structure or those comprising the imide compound and a transition metallic compound as catalysts for oxidizing substrates with molecular oxygen. These catalysts enable oxidation of an alkyl group bound to an aromatic ring under mild conditions. PCT International Publication Number WO 03/28884 and JP-A No. 2003-128618 each disclose a method of oxidizing an aromatic compound having an alkyl group or a lower-order oxidized group thereof on its aromatic ring with oxygen in the presence of a catalyst comprising an imide compound having a N-substituted cyclic imide skeleton to thereby yield a corresponding aromatic carboxylic acid. This method can produce an aromatic carboxylic acid without the need for special reaction facilities. Even this method, however, is still industrially insufficient in production conditions and productivity.